Ethylene bisdithiocarbamate (EBDC) fungicides, such as maneb and mancozeb, are important plant protection substances used for broad-spectrum disease control of more than 400 plant diseases in more than 70 crops (Ladovica, M., et. al. 2010. Plant Disease 94(9) 1076-1087. Mancozeb is especially important for controlling devastating and fast spreading diseases such as Late Blight of Potato caused by Phytophthora infestans, Apple scab caused by Venturia inaequalis, Downy mildew of grape caused by Plasmopara viticola and Sigatoka diseases of banana caused by various species of the genus, Mycosphaerella. Dithiocarbamate fungicides, especially mancozeb, are particularly useful for disease control because of their broad spectrum of activity, high tolerance by crop plants, and general usefulness for controlling fungal plant diseases resistant to certain fungicides that are active on only a single target site in the fungus.
Although EBDC fungicides are used widely, they have limitations due in part to the fact that many of them are in fact pre-fungicides and they do not exhibit significant anti-fungal activity until after they undergo conversion to a more fungicidal substance. For example, mancozeb is a pro-fungicide which, when exposed to water and oxygen, is rapidly converted to ethylene bisisthiocyanate sulfide (EBIS). Both oxygen and water are required in order to produce EBIS from EBDC fungicide. Sufficient oxygen for EBIS generation is present in the atmosphere. Sufficient water for EBIS generation can be provided by moisture in the forms of rain, dew, fog, mist, irrigation or periods of high humidity that may or may not be accompanied by free moisture. Once an EBDC fungicide has been applied to plants, EBIS generation is not limited by insufficient oxygen. However, the conversion of EBDC to EBIS may be limited by insufficient moisture. “Conversion” as used herein unless noted otherwise, means the formation of EBIS from EBDC by the reaction of EBDC with oxygen and water. While EBIS is the primary fungicidal toxicant produced from mancozeb, it remains present on the leaf surface at levels effective for disease control for only a short period of time, often with a half-life of less than 2 days. A study by Newsome (J. Agric. Food Chem. 1976(24), 999) reported that the degradation of mancozeb to EBIS reached peak levels about two days after application to tomato leaves.
The same general conditions leading to infection of plants by many fungal diseases also leads to the rapid generation and dissipation of fungicidal EBIS. Due to the relatively short period of their effectiveness under conditions conducive to plant disease, dithiocarbamates must often be re-applied at short intervals. Mancozeb also faces other practical use limitations. Previously, mancozeb was used in some European crops at rates as high as 2.8 kg of actual mancozeb per hectare. When mancozeb was re-registered in Europe, the maximum use rate was reduced to 1.6 kg per hectare. This regulation change has limited mancozeb's use on crops in Europe.
In order to improve the usefulness of dithiocarbamates for disease control, there is a need to increase the preventative effect of an individual application of the compound or to lengthen the time between applications, or both. Extensive modeling of mancozeb environmental fate in the phyllosphere has characterized the kinetics of EBIS generation from mancozeb on the leaf surface under a range of conditions conducive to fungal attack (Cryer, et. al. (Computers and Electronics in Agriculture (submitted for review/publication)). Cryer's model suggested that delaying the onset of the generation of EBIS from mancozeb or slowing its rate of release from mancozeb on the leaf surface would improve its disease control effectiveness. There appears to be little precedent in the published literature for controlling the actual conversion rate of a pro-pesticide into its active form on plant surfaces.
As reported herein, compositions that could modulate the reaction of mancozeb with water and oxygen to controllably release EBIS for an extended duration, may provide improvements such as 1) reducing the use rate of mancozeb necessary to control fungi, 2) extending the spray interval, 3) minimizing the degradation bi-product, i.e. ethylenethiourea (ETU).
Compositions and methods for modulating the rate of conversion of EBDC fungicides, such as mancozeb, into EBIS are disclosed herein. The described compositions suitable for providing improved disease control are comprised of an agriculturally effective amount of an EBDC fungicide, one or more EBIS-modulating polymers, one or more dispersants, and, optionally, other inert formulation ingredients.
In some exemplary embodiments, a fungicidal composition for modulating the conversion of an ethylene bisdithiocarbamate (EBDC) fungicide to ethylene bis-isothiocyanate sulfide (EBIS) is provided. The composition includes: an EBDC fungicide; an EBIS conversion-modulating polymer; and a dispersant. The EBDC fungicide is coated with the EBIS conversion-modulating polymer, such that the EBIS release half-life is increased by a factor of at least about 2 when compared to the uncoated EBDC fungicide.
In some exemplary embodiments of the fungicidal composition, the EBDC fungicide is at least one compound selected from the group consisting of: mancozeb, maneb, zineb and metiram. In a more particular embodiment, the EBDC fungicide is mancozeb.
In some exemplary embodiments of the fungicidal composition, the EBDC fungicide is in the form of solid particles. In a more particular embodiment, the EBDC fungicide is mancozeb.
In some exemplary embodiments of the fungicidal composition, the EBDC fungicide is distributed in a matrix of the EBIS conversion-modulating polymer. In a more particular embodiment, the EBDC fungicide is mancozeb.
In some exemplary embodiments of the fungicidal composition, the EBDC fungicide is in the form of crystals and/or solid particles and where the EBDC fungicides that are coated by the EBIS conversion-modulating polymer. In a more particular embodiment, the EBDC fungicide is mancozeb.
In some exemplary embodiments of the fungicidal composition, the EBDC fungicide produces ethylene bis-isothiocyanate sulfide (EBIS) when contacted with water and oxygen.
In some exemplary embodiments of the fungicidal composition, the EBIS conversion-modulating polymer provides a barrier to oxygen and/or water. In a more particular embodiment, the EBIS conversion-modulating polymer is at least one polymer selected from the group consisting of: a polyvinyl alcohol, a latex, a gelatin, a polyvinylpyrrolidone, a polyacrylate, a polyacrylamide, a polyvinylacetate, a polyvinylamine, a polyvinylsulfonate and mixtures and copolymers thereof. In a further more particular embodiment, the latex is selected from the group consisting of: standard or modified acrylic latex, standard or modified vinyl-acrylic latex, and styrene-acrylic latex. In another more particular embodiment, the polyvinyl alcohol is selected from partially hydrolyzed polyvinyl alcohols and co-polymers of partially hydrolyzed polyvinyl alcohols. An exemplary molecular weight range of the polyvinyl alcohol is from about 10,000 kDa to about 500,000 kDa and an exemplary degree of hydrolysis is from 60% to 99.9%. Another exemplary molecular weight range of the polyvinyl alcohol is from about 140,000 kDa to about 500,000 kDa and another exemplary degree of hydrolysis is from 87% to 99.9%.
In some exemplary embodiments of the fungicidal composition, the weight ratio of the EBIS conversion-modulating polymer to the EBDC fungicide in the composition is between about 1:200 to about 1:5.
In some exemplary embodiments of the fungicidal composition, the weight ratio of the EBIS conversion-modulating polymer to the EBDC fungicide is between 1:100 and 1:10.
In some exemplary embodiments of the fungicidal composition, the dispersant is at least one of the dispersant selected from the group consists of: sodium, calcium or ammonium lignosulfonate, alkyl naphthalene sulfonate condensate, ethylene oxide/propylene oxide block copolymer, tristyrylphenol ethoxylates styrene-acrylic copolymers, methylvinylether-maleic anhydride half ester copolymer, polyvinyl pyrrolidone, and a poly vinyl pyrrolidone copolymer.
In some exemplary embodiments of the fungicidal composition, the compound is in the form of a wettable powder.
In some exemplary embodiments of the fungicidal composition, the compound is in the form of a granule.
In some exemplary embodiments of the fungicidal composition, the compound is in the form of a water dispersible granule.
In some exemplary embodiments of the fungicidal composition, the compound is produced by a spray drying process.
In some exemplary embodiments, an aggregate solid particle is provided. The aggregate solid particle comprises an EBDC fungicide; a matrix or coating, wherein the matrix or the coating includes an EBIS conversion-modulating polymer, wherein the weight ratio of the EBIS conversion-modulating polymer to the EBDC fungicide is from about 1:200 to about 1:5, and wherein the EBIS conversion-modulating polymer is at least one polymer selected from the group consisting of: polyvinyl alcohol, latex, gelatin, polyvinylpyrrolidone, polyacrylate, polyacrylamide, polyvinylacetate, polyvinylamine, and polyvinylsulfonate; and a dispersant.
In some exemplary embodiments of the aggregarte solid particle, the EBDC fungicide is distributed in a matrix of the EBIS conversion-modulating polymer.
In some exemplary embodiments of the aggregarte solid particle, the EBDC fungicide is coated by the EBIS conversion-modulating polymer.
In some exemplary embodiments of the aggregarte solid particle, the particle is from about 1 to about 100 microns in size.
In some exemplary embodiments of the aggregarte solid particle, the EBDC fungicide is selected from the group consisting of: mancozeb, maneb, metiram, and zineb.
In some exemplary embodiments of the aggregarte solid particle, the latex is selected from the group consisting of: standard or modified acrylic latex, standard or modified vinyl-acrylic latex, and styrene-acrylic latex.
In some exemplary embodiments of the aggregarte solid particle, the polyvinyl alcohol is at least one polymer selected from the group consisting of: partially hydrolyzed polyvinyl alcohol, and a co-polymer of a partially hydrolyzed polyvinyl alcohol. In one more particular embodiment, the polyvinyl alcohol or the co-polymer of the polyvinyl alcohol has a molecular weight range from about 10,000 kDa to about 500,000 kDa and a degree of hydrolysis in the range of about 60% to about 99.9%. In another more particular embodiment, the polyvinyl alcohol has a molecular weight range from about 140,000 kDa to about 500,000 kDa and a degree of hydrolysis in the range of from about 87% to about 99.9%.
In some exemplary embodiments of the aggregarte solid particle, the dispersant is at least one dispersant selected from the group consisting of: sodium lignosulfonate, alkyl naphthalene sulfonate condensate, ethylene oxide/propylene oxide block copolymer, a tristyrylphenol ethoxylates styrene-acrylic copolymer, methylvinylether-maleic anhydride half ester copolymer, and polyvinyl pyrrolidone copolymer.
In some exemplary embodiments, a method of treating a plant is provided. The method includes applying to the surface of a plant or to a surface adjacent to the surface of a plant, an aqueous suspension of a fungicidally effective amount of an aggregate solid particle, wherein said particle is about 1 to about 100 microns in size and wherein said particle includes at least one EBDC fungicide and a matrix or a coating, wherein said matrix or said coating includes at least one EBIS conversion-modulating polymer, comprising at least one polymer selected from the group consisting of: polyvinyl alcohol, latex, gelatin, polyvinylpyrrolidone, polyacrylate, polyacrylamide, polyvinylacetate, polyvinylamine, and polyvinylsulfonate, and wherein the weight ratio of EBIS conversion-modulating polymer to EBDC fungicide weight ratio is from about 1:200 to about 1:5.
In some exemplary embodiments of the method of treating a plant, the EBDC fungicide is mancozeb.
In some exemplary embodiments of the method of treating a plant, the EBDC fungicide produces EBIS on the plant surface upon contact with water and/or oxygen.
In some exemplary embodiments of the method of treating a plant, the polyvinyl alcohol includes at least one polyvinyl alcohol selected from the group consisting of: partially hydrolyzed polyvinyl alcohol, and copolymer thereof.
In some exemplary embodiments of the method of treating a plant, the EBDC fungicide is embedded in a matrix of the EBIS conversion-modulating polymer.
In some exemplary embodiments of the method of treating a plant, the EBDC fungicide is coated with the EBIS conversion-modulating polymer.
In some exemplary embodiments of the method of treating a plant, the aqueous suspension is mixed either in concentrated or dilute form with a non-EBDC fungicide. In a more particular embodiment, the non-EBDC fungicide is effective on diseases caused by oomycete organisms.
In some exemplary embodiments, a method of increasing the efficacy of an EBDC fungicide for preventing or controlling fungal diseases on plant foliage under high humidity conditions is provided. The method includes applying a composition comprising an EBIS conversion-modulating polymer and the EBDC fungicide to at least one surface of plant; and exposing the surface of the plant to air, wherein the air is comprised of about 60% to about 95% relative humidity and at a temperature in the range of about 8 to about 33 degrees C.
In some exemplary embodiments, a method for extending the effective half-life of EBIS conversion from an EBDC fungicide particle is provided. The method includes providing a composition comprising at least one EBDC fungicide and an EBIS conversion-modulating polymer; and contacting said EBDC fungicide and EBIS conversion-modulating polymer composition with water and/or oxygen, wherein the ratio of the residence time of the polymer coated EBDC fungicide is increased by a factor of at least about 1.2 when compared to the uncoated EBDC fungicide as determined by the amount of EBIS produced over time.